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8. Early experiments in freeze-drying books and documents

8. 1 Precursors

8.1.1 Canadian entities

One of the first known reports on attempts to use freeze-drying for the salvage of water-damaged library materials was published after the Library of Parliament fire in Ottawa in August 1952. In order to extinguish the blaze sprinklers were kept on for six hours. As a result thousands of books were soaked or moistened. Experiments on drying were carried out by the Low Temperature Laboratory of the National Research Council and in the Forest Products laboratories of the Department of Resources and Development. Included among the methods tried were freeze-drying and vacuum-drying. The reported difficulty with these two methods was the slowness and relative inefficiency of attempting to dry the soaked books from the outside inwards (27).

8.1.2 Smithsonian institution, Washington, D.C.

Hower (23) of the Smithsonian Institution published a report on the freeze-dry preservation of biological specimens for exhibitions in museums. He describes a new application of the freeze-dry technique carried out in the 1960s after a copy of "Merchant's Almanac" was retrieved from a river steamer sunk in the Missouri River in 1865. The almanac had been submerged for over 100 years. It had been placed in a commercial deep freezer at about -20 C (-4 F). Dr. R.M. Organ, Chief of the Smithsonian's Conservation Analytical laboratory, asked Dr. Hower to experiment with part of the almanac to see if vacuum freeze-drying would work The specimen was placed in a large vacuum chamber at 20 C and the system pumped down to 150 microns (0.15mm Hg). The book was removed before it was totally dry in order that it have sufficient moisture to remain flexible. The initial weight of the specimen was 952.9 grams and final weight 522.9 grams. In the report Dr. Hower expresses his interest to work with more material of this type in the hope of establishing standard procedures.

8.1.3 Technical university of Denmark

Probably the first attempt to vacuum freeze-dry water damaged library materials with marked success was one carried out by Plink and Hoyer (18) in 1971. It all started during the winter of 1968 when a fire was being extinguished in the Greenland Regional Library of Godthab on the west coast of Greenland. Because of the weather conditions prevailing at the time, water from the fire hoses froze the water-soaked materials housed in the library. The most valuable items, packed in cardboard document cases, were hand-written letters, manuscripts and maps which belonged to a missionary of the midnineteenth century, Samuel Kleinschmidt (18). The frozen items were transported in that state to Copenhagen where they were kept in cold storage in order to have time to find the best course of action for the drying process.

The problem facing the technicians in Copenhagen was that the ink used in the documents would run if the conventional air-drying technique were to be used for thawing. The frozen books posed no problem and were air-dried. But it was determined that this technique was too risky for the manuscripts. The decision wee made to use freeze-drying.

The necessity for freeze-drying the documents was demonstrated by an experiment in which paper marked with various modern writing materials (ink, ball-point pen, felt tip marker) were immersed in water, frozen, and then either air or freeze-dried. The freeze-dried samples were perfect, whereas the writing on the air-dried samples had run.

Twenty-seven storage packets and a photograph album were delivered to the Food and Technology Laboratory of the Technical University of Denmark, Lyngby, where the freeze-dry chamber Atlas Ray 1) was located. The items were held at -70 C (-22 F) until the start of the freeze-dry operation. By careful manipulation the frozen packets were removed in order to eliminate a large resistance to mass transfer while undergoing freeze-drying.

To improve the rate of drying (for convenience rather than necessity) and to ensure sufficient clearance between the chamber's heater shelves, some of the thicker stacks of frozen documents were pried apart while frozen. This was possible without damage to the manuscripts only because paper folders had been used as separators within the library holder.

Stacks of frozen papers, two to three centimeters (about 3/4 to 1 1/14 inches) thick were placed on pre-cooled, porous trays and conservation freeze-drying conditions were chosen so that no melting or color change Would occur. Radiant heating at a plate temperature of 45 C (113 F) and a chamber pressure of 200 mtorr (0.2 mm Hg) was used. The weight of the sample was monitored by using the balance built into the freeze dryer; drying was continued to constant weight. The average drying time was about one and a half to two days. When drying was complete the chamber vacuum was slowly released (18).

Flink summarized the outcome of the operation as follows: The freeze-dry process gave perfect results as each page separated easily, and in no case did the ink run. Manuscripts which had been compressed and misshapened before freezing retained that shape after drying. These samples were later satisfactorily treated in the usual manner of pressing and binding. The photograph album (from 1906), freeze-dried at the same time, presented some problems. Prints which were frozen emulsion-to-emulsion often stuck together after drying. Soaking the stuck prints in water and then carefully separating under water usually solved this problem. Due to the thickness of the album (ten centimeters; about four inches), freeze-drying required four and a half days. Even with this length of time six photographs at the center of the album were still frozen and melted before they could be reins ten into the freeze-dryer, ruining the handwritten captions. This indicated that freeze-drying had indeed been necessary to conserve successfully the handwritten documents (28).


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